The present invention relates to a device for suction and collection of vehicle exhaust gases, to be carried out in particular on vehicle overhaul lines. Devices of this type can also advantageously be used in vehicle production plants.
Along the overhaul line, the vehicle, which is normally driven by its own engine, travels a short path in the garage, along which path there are various stations allocated to checking the emissions of the exhaust gases, the efficiency of the braking device, and the alignment of the steering equipment etc.
The purpose of the device which is the subject of the present invention is therefore to meet the need to suck the vehicle exhaust gases as they are emitted, following the vehicle during its displacements in the garage in which the said checks are carried out.
The devices of this type which are currently commercially available comprise a flexible tube, which is attached at one end to the exhaust pipe of the vehicle in transit, which tube is supported by a carriage suspended above the corresponding vehicle, such as to suck the exhaust gases produced, directly by means of an appropriate suction device.
In a complete operating cycle, a device of the type described comprises a first step, in which the vehicle itself drives the carriage by means of the suction tube, and a second step, in which, when the overhaul is completed, the end of the suction tube is automatically released from the exhaust pipe, and the carriage is returned to the beginning of the line by means of an appropriate movement device.
In other words, the operating cycle consists of two separate steps, i.e. a first, outward step, in which the carriage can freely run on the rail, driven by the vehicle itself , and a second step in which the carriage and the corresponding flexible tube are returned to the starting point by means of a drive device. The drive is switched on and off automatically as soon as the carriage passes over appropriate limit switches disposed on the line. In this type of system, all the operations are automated, and the operator does not have to intervene in any way. Normally, the flexible tube is raised during the return step by means of an appropriate raising device, in order to increase the safety of employees who may be present in the garage.
In some models, in the return step of the carriage, there is use of a drive wheel which is connected to this carriage, and is rotated by a corresponding drive device. In this return step, the drive wheel, which is normally of the friction type, can roll on an appropriate track which runs parallel to the slotted suction duct, whereas in the preceding, outward step, the friction wheel is moved away from the track, such that driving of the carriage by the vehicle, by means of the flexible tube, is not impeded by the resistance created by the gears which are present in the drive device.
A solution of this type is represented for example in European patent EP-B2-0 174 481 (JENZSCH et al.), in which the carriage is provided with a friction wheel, which is keyed directly onto the output shaft of an electric motor. The friction wheel and the corresponding motor are supported by a support which is pivoted such that rotation of this support, induced by the action of a magnetic device, makes the friction wheel engage on an appropriate track provided. The carriage can thus be moved by means of the electric motor, which, by transmitting motion to the friction wheel, which is now engaged with the track, induces consequent movement of the entire carriage. On the other hand, in the outward step, the same magnetic device rotates in the opposite direction the support which supports the motor and the friction wheel, thus moving the latter away from the guide.
Although this system has undeniable advantages compared with those of the prior art, it does not meet the requirements of simplicity and convenience which these mechanisms should have. In fact, the assembly which is constituted by the magnetic device and by the motor assigned for movement of the friction wheel, is very large, and requires a housing with large dimensions. In addition, as well as having the strength necessary to guarantee secure contact between the friction wheel and the track, the magnetic device must also support the suspended weight of this friction wheel and of the corresponding motor. Inter alia, the range of the rod of the magnetic device must be sufficient to guarantee efficient adherence and efficient detachment of the friction wheel from the track, in the two operating steps.
The two conditions previously described together require use of a very high-power magnetic device, with a consequent excess size of the supply system, and in particular of the electric transformer for the low voltage, with a corresponding increase in the overall cost of the system.
In addition, the device described in European patent EP-B2-0 174 481 can also be used as a system for braking the carriage, by supplying power to the magnetic device alone, which thrusts the friction wheel against the corresponding guide. In this operating condition the electric motor, on the shaft of which the friction wheel is keyed, is not operating. The entire carriage is therefore braked by dragging the friction wheel on the guide, since the wheel can no longer roll on the latter because it is locked by the gears which are present in the gear motor. This means that during the breaking step, the entire device acts in a manner which is not ideal, since it leads to localised wear in some areas of the friction wheel. A further consequence of this unsatisfactory operation consists in the fact that the supply voltage of the magnetic device is varied in order to modulate the braking; thus, if the voltage is not regulated satisfactorily, there is a risk either of supplying low force, which is insufficient to raise the gear motor and the wheel, or of supplying excessive force, which causes a sudden stoppage of the carriage and of the corresponding movement devices.